PDF compression guides

OCR Text Layers and PDF Compression

Validate both the visible scan and the invisible text behavior.

By PDFStay Editorial Team

Last updated

OCR can add searchable text behind scanned page images, but that text layer does not replace the image that readers see. Compression may reduce the image data while the OCR layer remains, or a conversion may damage search and copy behavior. After processing an OCR PDF, search for several visible phrases, copy text from different pages, and inspect whether the results still match the scan.

What does an OCR text layer contribute?

OCR records recognized characters and their positions so a viewer can search or select text over an image. Recognition errors, reading order, and character mapping can remain imperfect even when the page looks correct.1, 2, 3

Decision guide for ocr text layers and pdf compression
SituationPractical actionWhat to verify
Search is importantUse conservative processingSearch multiple distinctive phrases1
Only visual pages are requiredConfirm the destination accepts image-only PDFsDo not imply accessibility from appearance alone2

How should you verify the final PDF?

  1. Keep the original file unchanged and work from a clearly named copy.
  2. Compare search hits, copied text, page order, and the smallest scanned details with the original.1
  3. Open the exact downloaded file in a second viewer before sending or uploading it.
  4. Save the destination receipt or delivery evidence when the document matters.

FAQ

Can a PDF look correct while its OCR text is wrong?

Yes. The visible scan can remain unchanged while search results, copied text, character mapping, or reading order are inaccurate.

Does OCR make a scanned PDF accessible?

Not by itself. OCR can add searchable text, but accessibility also depends on structure, reading order, language, alternatives, and manual remediation.

Sources

  1. U.S. National Archives — Scanned Images of Textual Recordsgovernment technical guidanceSource reviewed:
  2. FADGI — Technical Guidelines for Digitizing Cultural Heritage Materialsgovernment technical guidanceSource reviewed:
  3. PDFStay — Compress PDF workflowPDFStay first-party methodologySource reviewed: